S1·E1 "K-9" or "The Secret File of the Masticated Mongrel"

Ralph is alerted by the secret headquarters that a strange epidemic of people hating their dogs is spreading around, and he seeks the help of French poodle, Agent Noodle, the master of fuzzy logic. Once Agent Noodle discovers that the epidemic is being spread by a strange chemical in the human snack foods, Ralph, Noodle, and Mitzy travel to Angus' Labratory, where Ralph undergoes scrupulous training to go undercover as a cat at the Notneb Kitty-Litter Factory, where there's been rumors of cats roaming around. While there, Ralph discovers that the cats are putting the chemical, K-9, in the snack foods, and is joined by Mitzy and other spy dogs to defeat the cats.